act: remove rtnl_act_alloc_cache()

It is complicated to cache tc actions, they are different
from tc qdisc's and filters by design. So, it is simple
if we just don't cache them.

This patch only removes the tc action cache allocation API.
We still need to bypass the libnl cache layer from scratch,
but that would not break ABI any more, therefore we can do
it later.

Cc: Thomas Graf <tgraf@suug.ch>
Cc: Thomas Haller <thaller@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Thomas Haller <thaller@redhat.com>